Physiology, MBBS Second Year. This chapter is split into 7 topics and has
307 practice questions. The topics covered are listed below, followed by
10 free sample questions from the chapter.
Topics in this chapter
Normal body temperatures & the balance of heat production and heat loss47 questions
Body insulation, blood flow, heat transfer & sympathetic control43 questions
Methods of heat loss: radiation, conduction, convection & evaporation49 questions
Sample questions: Body Temperature Regulation and Fever
10 sample questions with the correct answer and an explanation. Try to answer each one before reading the explanation.
Q1. Which factors affect metabolic heat production?
A. Only basal metabolic rate
B. Only environmental temperature
C. Only muscle activity
D. Basal metabolic rate, muscle activity including shivering, thyroxine/growth hormone/testosterone, epinephrine/norepinephrine and sympathetic stimulation, increased chemical activity with higher cell temperature, and the thermogenic effect of food(correct answer)
Answer: D.Metabolic heat production is affected by the basal metabolic rate of body cells, muscle activity including shivering, thyroxine, growth hormone and testosterone, epinephrine/norepinephrine and sympathetic stimulation, increased chemical activity with higher cell temperature, and the thermogenic effect of food.
Q2. Assertion: Body temperature is a balance between heat production and heat loss. Reason: Heat is generated continuously by metabolism and must be lost to the surroundings to maintain a stable core temperature.
A. Both Assertion and Reason are true, and the Reason correctly explains the Assertion(correct answer)
B. Assertion is true but Reason is false
C. Assertion is false but Reason is true
D. Both are true, but the Reason does not explain the Assertion
Answer: A.Body temperature control is the balance of heat production (a by-product of metabolism, generated mainly in the liver, brain, heart and muscles) against heat loss (transfer of heat from core to skin and then to the environment), keeping core temperature constant within about 1°F.
Q3. Why does the body need both heat-producing and heat-losing mechanisms?
A. Because heat loss is constant regardless of the environment
B. Because core temperature is allowed to vary widely
C. Because heat production is absent at rest
D. Because metabolic heat production is continuous and varies with activity, hormones and food intake, while heat loss must match it to keep core temperature constant within about 1 degree F — even over environmental extremes of 55 to 130 degrees F in dry air(correct answer)
Answer: D.Heat is continuously produced as a by-product of metabolism — varying with basal metabolic rate, muscle activity, thyroxine/growth hormone/testosterone, sympathetic activity and the thermogenic effect of food — and generated mainly in the liver, brain, heart and muscles. To keep core temperature constant within about 1°F over environmental extremes (55–130°F in dry air), heat transfer from core to skin and skin to environment must be adjusted, with skin temperature varying to serve heat loss.
Q4. Why is skin blood flow such an effective means of controlling heat loss?
A. Because skin blood flow is constant
B. Because fat conducts heat efficiently
C. Because the skin generates most body heat
D. Because skin blood flow can vary from near zero to about 30 percent of cardiac output under sympathetic vasoconstrictor control, so heat carried from the core to the skin can be adjusted over a wide range on top of the insulating effect of skin, subcutaneous tissue and fat — with the hypothalamus coordinating the response(correct answer)
Answer: D.The skin is the principal heat-exchange surface: its blood flow can range from near zero to about 30% of cardiac output under sympathetic vasoconstrictor control, allowing heat transfer from the core to be varied widely. This sits atop the insulation provided by skin, subcutaneous tissue and fat (fat conducting heat only about one third as well as other tissues, with better insulation in women), while the AV anastomoses of the hands, feet and ears and the subcutaneous venous plexus further augment heat exchange; the hypothalamus coordinates the whole system.
Q5. Assertion: At environmental temperatures above skin temperature, evaporation becomes the only avenue of heat loss. Reason: Radiation and conduction cease to remove heat when the surroundings are hotter than the body.
A. Both are true, but the Reason does not explain the Assertion
B. Assertion is false but Reason is true
C. Both Assertion and Reason are true, and the Reason correctly explains the Assertion(correct answer)
D. Assertion is true but Reason is false
Answer: C.Because radiation and conduction depend on a temperature gradient from body to surroundings, they stop removing heat when air temperature exceeds skin temperature; evaporation (which depends on water vapour pressure, not the temperature gradient) then becomes the only means of heat loss.
Q6. Why does the relative importance of the heat-loss mechanisms change with environmental conditions?
A. Because radiation works best in hot air
B. Because all mechanisms operate equally under every condition
C. Because radiation and conduction depend on a temperature gradient (about 40 percent and about 15 percent respectively at room temperature) and fail when the environment is hotter than the skin, whereas evaporation (about 22 percent, plus insensible loss of 16 to 19 Cal/hour) depends on water vapour pressure and becomes the sole avenue of heat loss at high temperature — and wind, water immersion and wet clothing further modify loss(correct answer)
D. Because evaporation is the main mechanism in the cold
Answer: C.At room temperature heat is lost mainly by radiation (about 40%), evaporation (about 22%, including insensible loss of 16–19 Cal/hour or 600–700 ml/day) and convection (about 15%), with conduction contributing about 3% to solids and 15% to air. But radiation and conduction require a favourable temperature gradient: when air temperature exceeds skin temperature they cease to remove heat and evaporation — which depends on water vapour pressure — becomes the only route. Wind increases loss (proportional to the square root of wind velocity) and water immersion increases it further because water has higher specific heat and conductivity, while wet clothing loses insulation about 20 times faster than dry clothing.
Q7. Why is sweating both an effective cooling mechanism and a threat to salt balance?
A. Because sweating reduces heat loss
B. Because sweat is protein-rich and cools by conduction
C. Because evaporating sweat removes large amounts of heat (the sole avenue of heat loss when the environment is hotter than the skin), but the salty primary sweat loses sodium chloride — about 50 to 60 mEq/L at high rates — until acclimatization raises aldosterone and reduces loss from 15 to 30 g/day to 3 to 5 g/day(correct answer)
D. Because sweat contains no sodium
Answer: C.Sweating is the crucial route of evaporative heat loss — indispensable when radiation and conduction fail at high environmental temperature — with output rising to 2–3 L/hour after acclimatization. But the primary sweat resembles plasma and remains salty at high flow rates (about 50–60 mEq/L sodium chloride, 15–30 g/day loss), so acclimatization over 1–6 weeks raises aldosterone to conserve salt, reducing loss to 3–5 g/day while preserving the improved cooling capacity.
Q8. Assertion: The hypothalamus is the central controller of body temperature. Reason: It contains heat- and cold-sensitive neurons in the anterior preoptic area and an integrative centre in the posterior hypothalamus.
A. Both Assertion and Reason are true, and the Reason correctly explains the Assertion(correct answer)
B. Both are true, but the Reason does not explain the Assertion
C. Assertion is false but Reason is true
D. Assertion is true but Reason is false
Answer: A.Temperature regulation is mediated by nervous feedback via the hypothalamus: the anterior hypothalamic-preoptic area contains heat- and cold-sensitive neurons (heating it causes sweating and vasodilation), while the posterior hypothalamus integrates these and peripheral signals and controls heat production and heat conservation responses.
Q9. Which statement about the anatomical organisation of thermoregulatory centres is TRUE?
A. Only the skin is involved
B. Sensing and heat-loss responses are associated mainly with the anterior hypothalamic-preoptic area, while integration and heat-conservation responses are associated with the posterior hypothalamus(correct answer)
C. Both sensing and integration occur in the spinal cord
D. Both sensing and integration occur in the posterior hypothalamus
Answer: B.The anterior hypothalamic-preoptic area contains the heat- and cold-sensitive neurons (with heating causing sweating and vasodilation), while the posterior hypothalamus integrates temperature signals and controls heat production and heat conservation responses.
Q10. Why is the hypothalamus uniquely suited to control body temperature?
A. Because it contains only cold-sensitive neurons
B. Because it contains both heat-sensitive and cold-sensitive neurons in the anterior preoptic area, receives input from skin receptors (cold receptor predominant, about 10:1) and deep body receptors in the spinal cord, viscera and great veins, and its posterior region integrates these signals to control heat production and heat conservation — maintaining core temperature within about 1 degree F over an enormous environmental range(correct answer)
C. Because it acts independently of the skin
D. Because it receives no peripheral input
Answer: B.The hypothalamus combines intrinsic sensing (heat- and cold-sensitive neurons of the anterior hypothalamic-preoptic area) with peripheral input from skin receptors (with about 10 times more cold than warmth receptors) and deep body receptors (spinal cord, abdominal viscera, great veins, mainly detecting cold). Its posterior region integrates these signals to control heat production and heat conservation responses, while heating the anterior area evokes sweating and vasodilation — enabling a nude person to keep core temperature within about 1°F in dry air from 55 to 130°F.